Methods for the inhibition of cancer metastasis mediated by endothelial adhesion molecules

ABSTRACT

Methods and compositions are disclosed for the inhibition of cancer metastases mediated by endothelial adhesion molecules. The present invention discloses that sialyl Le a  and di-sialyl Le a , which are expressed at the surface of cancer cells, function as a binding partner for LEC-CAMs, such as ELAM-1, which are expressed at the surface of endothelial cells. The present invention also discloses that LEC-CAMs, such as ELAM-1, involved in cancer metastasis share a carbohydrate domain common to both sialyl Le a  and sialyl Le x . Antibodies, saccharides, glycoconjugates, enzyme inhibitors and other compounds may be used in the methods of the present invention to inhibit the binding of malignant cells to endothelial cells for a variety of purposes in vivo and in vitro.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No. 07/721,771, filed Jun. 25, 1991, abandoned; which application is a continuation-in-part of U.S. patent application Ser. No. 07/688,037, filed Apr. 19, 1991, abandoned.

TECHNICAL FIELD

The present invention is generally directed toward the inhibition of cancer metastasis mediated by endothelial adhesion molecules, and more specifically, toward such inhibition through the use of saccharides, glycoconjugates, antibodies, enzyme inhibitors, and other agents which disrupt such binding of cancer cells to endothelia.

BACKGROUND OF THE INVENTION

Despite enormous investments of financial and human resources, cancer remains one of the major causes of death. Current cancer therapies cure only about fifty percent of the patients who develop a malignant tumor. In most human malignancies, metastasis is the major cause of death.

Metastasis is the formation of a secondary tumor colony at a distant site. It is a multistep process of which tumor invasion is an early event. Tumor cells locally invade host tissue barriers, such as the epithelial basement membrane, to reach the interstitial stroma, where they gain access to blood vessels ("hematogenous metastasis") or lymphatic channels for further dissemination. After invading the endothelial layer of a vessel wall, the circulating tumor cells are dislodged into the circulation and arrest in the precapillary venules of the target organ by adherence to endothelial cell lumenal surfaces, or exposed basement membranes. The tumor cells again invade the vascular wall to enter the organ parenchyma. Finally, the extravasated tumor cell grows in a tissue different from where it originated.

Most cancer cells fail to survive in the circulation and it appears that normally the lining of blood vessels acts as a barrier to tumor cell extravasation. Endothelial injury or perturbation increases tumor metastasis. In addition, certain factors, such as cytokines, have been shown to substantially increase the adhesion of cancer cells to treated endothelium in vitro. Interleukin 1 (IL-1) and tumor necrosis factor (TNF), which are cytokines, each stimulate the biosynthesis and expression of a cell surface receptor called ELAM-1 (endothelial leukocyte adhesion molecule). ELAM-1 is a member of a family of calcium-dependent cell adhesion receptors, known as LEC-CAMs or selecting, which includes LECAM-1 and GMP-140 (also known as PADGEM or CD62). During an inflammatory response, ELAM-1 on endothelial cells functions as a "homing receptor" for leukocytes. Recently, ELAM-1 on endothelial cells was shown to mediate the increased adhesion of colon cancer cells to endothelium treated with cytokines (Rice and Bevilacqua, Science 246:1303-1306, 1989).

In most human malignancies, distant metastases are often too small to be detected at the time the primary tumor is treated. Furthermore, widespread initiation of metastatic colonies usually occurs before clinical symptoms of metastatic disease are evident. The size and age variation in metastases, their dispersed anatomical location, and their heterogeneous composition are all factors that hinder surgical removal and limit the concentration of anticancer drugs that can be delivered to the metastatic colonies. It has been estimated, for example, that in 1991 there will be over 60,000 deaths and over 150,000 new cases from just colorectal cancer in the U.S. alone.

Due to the difficulties in the current approaches to the treatment and prevention of metastases, there is a need in the art for improved methods and compositions for inhibiting metastasis mediated by endothelial adhesion molecules. The present invention fills this need, and further provides other related advantages.

SUMMARY OF THE INVENTION

Briefly stated, the present invention provides methods and compositions for the inhibition of cancer metastasis mediated by endothelial adhesion molecules. In one aspect, the present invention provides methods for inhibiting, within a biological preparation, the binding of malignant cells expressing sialyl Le^(a) or di-sialyl Le^(a), to endothelial cells. In one embodiment, the method comprises incubating the biological preparation with at least one agent that inhibits the binding of malignant cells expressing sialyl Le^(a) or di-sialyl Le^(a), to endothelial cells expressing a LEC-CAM. In another embodiment, the method comprises incubating the biological preparation with at least one agent that inhibits the binding of malignant cells expressing sialyl Le^(a) or di-sialyl Le^(a), to endothelial cells expressing ELAM-1. In another embodiment, the method comprises incubating the malignant cells with at least one enzyme inhibitor that inhibits the biosynthesis of sialyl Le^(a) or di-sialyl Le^(a) by the malignant cells.

In another aspect of the present invention, methods are provided for inhibiting the spread of malignant cells expressing sialyl Le^(a) or di-sialyl Le^(a), to secondary sites in a warm-blooded animal. In one embodiment, the method comprises administering to a warm-blooded animal an effective amount of at least one agent that inhibits the binding of malignant cells expressing sialyl Le^(a) or di-sialyl Le^(a), to endothelial cells expressing a LEC-CAM. In another embodiment involving hematogenous metastasis, the method comprises administering to a warm-blooded animal an effective amount of at least one agent that inhibits the binding of malignant cells expressing sialyl Le^(a) or di-sialyl Le^(a), to endothelial cells expressing ELAM-1. In another embodiment, the method comprises administering to a warm-blooded animal an effective amount of at least one enzyme inhibitor that inhibits the biosynthesis of sialyl Le^(a) or di-sialyl Le^(a) by the malignant cells.

In a related aspect, methods are provided for inhibiting within a biological preparation the binding of malignant cells expressing sialyl Le^(a), di-sialyl Le^(a) or sialyl Le^(x), to endothelial cells. In one embodiment, the method comprises incubating a biological preparation, containing endothelial cells expressing a LEC-CAM, with at least one agent capable of reacting with both sialyl Le^(a) and sialyl Le^(x). In another embodiment, the method comprises incubating a biological preparation, containing endothelial cells expressing ELAM-1, with at least one agent capable of reacting with both sialyl Le^(a) and sialyl Le^(x).

In another related aspect, methods are provided for inhibiting the spread of malignant cells expressing sialyl Le^(a), di-sialyl Le^(a) or dialyl Le^(x), to secondary sites in a warm-blooded aminal. In one embodiment, the method comprises administering to a warm-blooded animal an effective amount of at least one agent capable of reacting with both sialyl Le^(a) and sialyl Le^(x). In another embodiment involving hematogenous metastasis, the method comprises administering to a warm-blooded animal an effective amount of at least one agent capable of reacting with both sialyl Le^(a) and sialyl Le^(x).

These and other aspects of the present invention will become evident upon reference to the following detailed description and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 describes pictorially a cell binding assay used to assess binding of ELAM-1 transfected cells to neoglycoproteins.

FIG. 2 graphically illustrates the relative binding of ELAM-1 transfected cells to certain neoglycoproteins.

FIG. 3 graphically illustrates the relative binding of ELAM-1 transfected cells to certain neoglycoproteins.

DETAILED DESCRIPTION OF THE INVENTION

Prior to setting forth the invention, it may be helpful to an understanding thereof to set forth definitions of certain terms to be used hereinafter.

Antibody--as used herein, includes both monoclonal and polyclonal antibodies and may be an intact molecule, a fragment thereof, or a functional equivalent thereof. The antibody may be genetically engineered. Examples of antibody fragments include F(ab')₂, Fab', Fab and Fv.

Saccharide--as used herein, includes oligosaccharides, and may be naturally derived, synthetically prepared, portions of either, and derivatives of any of the foregoing.

Glycoconjugate--as used herein, includes a saccharide which is coupled to a non-saccharide molecule, e.g., a lipid or a polypeptide.

As noted above, the present invention is generally directed towards methods and compositions for the inhibition of cancer metastasis mediated by endothelial adhesion molecules. More specifically, the disclosure of the present invention shows that antibodies, saccharides, glycoconjugates therefrom or enzyme inhibitors may be used to inhibit the binding of malignant cells to endothelial cells for a variety of purposes in vivo and in vitro.

As described above, metastasis is a multistep process. During metastasis, cancer cells circulate through the microvascular and lymph systems and then migrate through the walls of the blood or lymph vessels to establish a new and aggressive tumor at a secondary organ site. A critical step in the metastasis process is the adherence of circulating cancer cells to the endothelial lining of blood vessel or lymph vessel walls. As disclosed within the present invention, the carbohydrates sialyl Le^(a) and di-sialyl Le^(a), which are expressed at the surface of certain cancer cells, function as a ligand (i.e., binding partner) for LEC-CAMs, such as ELAM-1, which are expressed at the surface of endothelial cells. Therefore, for those cancer cells, metastasis involves the adherence of cancer cells to the endothelial cells via the binding of sialyl Le^(a) and/or di-sialyl Le^(a) on the cancer cells to adhesion molecules on endothelial cells. Other cancer cells express predominantly sialyl Le^(x), or sialyl Le^(x) and sialyl Le^(a) (and/or di-sialyl Le^(a)). The present invention discloses that LEC-CAMs, such as ELAM-1, share a carbohydrate domain common to both sialyl Le^(a) and sialyl Le^(x) on malignant cells, and therefore agents can be produced which are capable of binding to both. Inhibition of the initial binding event between LEC-CAMs and sialylated structures by the methods of the present invention prevents the adhesion of metastatic cells to the endothelial lining of blood or lymph vessel walls, thereby eliminating the spread of metastatic cells to secondary organs. Suitable blocking agents include those which inhibit the binding of malignant cells expressing sialyl Le^(a), di-sialyl Le^(a), or sialyl Le^(x), to endothelial cells expressing LEC-CAM adhesion molecules such as ELAM-1. Representative agents include antibodies, saccharides and glycoconjugates therefrom.

The antibodies employed in the present invention may be polyclonal or monoclonal antibodies. Briefly, polyclonal antibodies may be produced by immunization of an animal and subsequent collection of its sera.

Immunization is accomplished, for example, by a systemic administration, such as by subcutaneous, intrasplenic or intramuscular injection, into a rabbit, rat or mouse. It is generally preferred to follow the initial immunization with one or more booster immunizations prior to sera collection. Such methodology is well known and described in a number of references.

Monoclonal antibodies (MAbs) suitable within the present invention include those of murine or human origin, or chimeric antibodies such as those which combine portions of both human and murine antibodies (i.e., antigen binding region of murine antibody plus constant regions of human antibody). Human and chimeric antibodies may be produced using methods known by those skilled in the art. Human antibodies and chimeric human-mouse antibodies are advantageous because they are less likely than murine antibodies to cause the production of anti-antibodies when administered clinically.

MAbs may be generally produced by the method of Kohler and Milstein (Nature 256:495-497, 1975; Eur. J. Immunol. 6:511-519, 1976). Briefly, the lymph nodes and/or spleens of an animal immunized with sialyl Le^(a) or di-sialyl Le^(a) are fused with myeloma cells to form hybrid cell lines ("hybridomas" or "clones"). Each hybridoma secretes a single type of immunoglobulin and, like the myeloma cells, has the potential for indefinite cell division. It may be desirable to couple such molecules to a carrier to increase their immunogenicity. Suitable carriers include keyhole limpet hemocyanin, thyroglobulin, bovine serum albumin and derivatives thereof. An alternative to the production of MAbs via hybridomas is the creation of MAb expression libraries using bacteriophage and bacteria (e.g., Sastry et al., Proc. Natl. Acad. Sci USA 86:5728, 1989; Huse et al., Science 246:1275, 1989). Selection of antibodies exhibiting appropriate specificity may be performed in a variety of ways which will be evident to those skilled in the art. Typically, such antibodies will selectively bind with an affinity of about 10⁷ liters/mol or higher.

Representative examples of MAbs suitable within the present invention include N-19-9 and HECA-452 for sialyl Le^(a), and FH-7 for di-sialyl Le^(a). MAb N-19-9 is available from ATCC (American Type Tissue Collection, Rockville, Md.) as ATCC HB 8059 or may be produced as described in U.S. Pat. No. 4,471,057 (and Somatic Cell Genet. 5:957-971, 1979; J. Biol. Chem. 257:14365, 1982). MAb HECA-452 may be produced according to Duijvestijn et al., Am. J. Path. 130:147-155, 1988. FH-7 may be produced according to Nudelman et al., J. Biol. Chem. 261:5487, 1986.

In addition to antibodies which are capable of binding to sialyl Le^(a), di-sialyl Le^(a) or sialyl Le^(x), saccharides and glycoconjugates therefrom may also inhibit the binding of metastatic cells expressing sialyl Le^(a), di-sialyl Le^(a) or sialyl Le^(x), to endothelia. As used herein, the terms "sialyl Lea^(a) " and "di-sialyl Lea^(a) " represent structures I and II, respectively, as follows: ##STR1## Neu5Ac represents sialic acid; Gal represents galactose; GlcNAc represents N-acetyl-glucosamine; Fuc represents fucose and R is typically a ceramide (with a glucose residue interposed) or a protein. Sialyl Le^(x) is an isomer of sialyl Le^(a) wherein the Gal-GlcNAc linkage is β1-4 and the Fuc-GlcNAc linkage is α1→3. Saccharides suitable within the present invention include the carbohydrate portion of sialyl Le^(a) or di-sialyl Le^(a) (i.e., formula I or II minus R), and derivatives of either, including those which cross-react with both sialyl Le^(a) and sialyl Le^(x) Derivatives of these compounds include substitution of individual saccharide residues with other saccharide residues and/or with non-saccharide molecules such as hexyl rings without hydroxyl groups. For example, the internal GlcNAc may be replaced with another saccharide residue such as a glucose (Glc). Alternatively (or in addition to substitutions), the carbohydrate portion of sialyl Le^(a), di-sialyl Le^(a), or derivatives thereof, may be truncated by deletion of one or more saccharide residues. For example, a tetrasaccharide may be created with the structure: ##STR2## Given the teachings described herein, it will be evident to those skilled in the art that other saccharides will be suitable within the present invention.

A saccharide may be coupled to a non-saccharide molecule to form a glycoconjugate. For example, a saccharide may be linked to a polyacrylamide. Alternatively, a saccharide may be linked to a lipid. Typical lipids include ceramide, i.e., sphingolipid bases which are acylated on the amine with a fatty acid. For example, sialyl Le^(a), di-sialyl Le^(a), or a saccharide cross-reaction with sialyl Le^(a) and sialyl Le^(x) may be linked to a ceramide. Alternatively, a saccharide may be bonded to an amino acid or an amino acid-containing molecule, such as a peptide, a polypeptide or a protein. Saccharides are naturally linked to an amino acid or amino acid-containing molecule via the hydroxyl group of a serine or threonine amino acid residue, but can also be linked through other groups such as an amino group.

Saccharides and glycoconjugates provided by the present invention may be represented by structures III and IV as follows: ##STR3## R includes H, OH, lipid, ceramide, or one or more amino acids; x, y and z are independently selected from saccharides, or either y or z or both may be absent.

Numerous methods for preparing saccharides and glycoconjugates are well known to those skilled in the art. Saccharides may be prepared synthetically using chemical, and/or enzymatic, reagents and techniques. For example, sialyl Le^(a) saccharides have been prepared by enzymatic synthesis (e.g., Palcic et al., Carbohydr. Res. 190:1-11, 1989). Glycoconjugates may be prepared, for example, through reductive amination. The method of Zopf et al. (Meth. Enzymol. 50:171-175, 1978; Jeffrey et al., Biochem. Biophys. Res. Commun. 62:608-613, 1975) involves 4-aminophenethylamine derivatives of saccharides via reductive amination using sodium borohydride. In brief, sugars are first reacted with the amino reagent by dissolving them in the neat reagent for 15 hours. Sodium borohydride in ethanol is then added. After 5 hours, the product is separated from the reagent by gel filtration and ion exchange chromatography. The derivatives may then be coupled to a molecule containing a group which is reactive with amines. The same amine derivative may be coupled to saccharides using sodium cyanoborohydride. (Svensson et al., J. Immunol. Meth. 25:323-335, 1979). In brief, a sugar is dissolved in water, and the same volume of amine (a 170-fold molar excess) is added together with sodium cyanoborohydride (a ten-fold molar excess). The reduction is performed at pH 8 for 48 hours, and the product purified by gel chromatography. Coupling to different molecules, such as proteins, may be performed by the isothiocyanate coupling method.

Another example of a reagent suitable for preparing glycoconjugates by reductive amination is p-trifluoroacetamidoaniline (TFAN). The reductive amination reaction is carried out in aqueous solution overnight at pH 5-6 with sodium cyanoborohydride as the reducing agent. Typically, a 5-fold excess of TFAN is used. TFAN-derivatized saccharides are generally protected from oxidation by N-acetylation, e.g., by treatment with methanolic acetic anhydride, to yield TFAc-derivatives. Prior to conjugation, the N-trifluoroacetamido protective group is removed by treatment of the TFAc derivative with aqueous ammonia or 0.5 M sodium hydroxide for 3 hours. Conjugation of the derivatives to molecules, for example to proteins such as bovine serum albumin (BSA), may be achieved by isothiocyanate coupling methods. Other examples of suitable reagents and reactions include p-tetradecylaniline derivatives of saccharides and the preparation of aminoalditols by oxidation of saccharide TFAN derivates with cerium ammonium sulfate (Lindenberg et al., J. Reprod. Fert. 89:431-439, 1990).

The inhibition of the binding of cancer cells expressing sialyl Le^(a), di-sialyl Le^(a) or sialyl Le^(x), to endothelia has a variety of in vitro and in vivo uses. Sialyl Le^(a) and di-sialyl Le^(a) are type 1 carbohydrate chains (i.e., have a Galβ1→3GlcNAc polylactosamine unit structure) and sialyl Le^(x) is a type 2 carbohydrate chain (i.e., has a Galβ1→4 GlcNAc polylactosamine unit structure. A number of cancer cells, such as colorectal and pancreatic, have a prevalence of type 1 carbohydrate chains including sialyl Le^(a) and di-sialyl Le^(a). Other cancer cells, such as breast, lung and ovarian, have a prevalence of type 2 carbohydrate chains including sialyl Le^(x).

Regarding in vitro aspects, as noted above, the present invention provides methods for inhibiting the binding of cancer cells to endothelia in a biological preparation. Representative examples of biological preparations include blood vessel and/or lymph vessel endothelia in combination with a malignancy. The endothelia and the malignancy may be in the form of tissue or cells removed from an organism, or cultured cells. In one embodiment, the method comprises incubating a biological preparation, which contains malignant cells expressing sialyl Le^(a), di-sialyl Le^(a) or sialyl Le^(x) and endothelial cells expressing a LEC-CAM, with an effective amount of at least one agent, such as an antibody, saccharide or glycoconjugate as described above. In another embodiment, the method comprises incubating malignant cells with at least one enzyme inhibitor that inhibits the biosynthesis of sialyl Le^(a) or di-sialyl Le^(a) by the cells. Suitable enzyme inhibitors include inhibitors of glycosyltransferases. Representative examples of inhibitors for glycosyltransferases include inhibitors for fucosyltransferases (e.g., as described by Palcic et al., J. Biol. Chem. 264:17174-17181, 1989), for N-acetylglucosaminyltransferases (e.g., as described by Palcic et al., J. Biol. Chem. 265:6759-6769, 1990), and for sialyltransferases (e.g., as described by Broquet et al., J. Neurochem. 54:388-394, 1990; Karaivanova et al., Cancer Biochem. Biophys. 11:311-315, 1990).

The present invention also provides methods for inhibiting metastasis in a warm-blooded animal such as a human. In one embodiment, the method comprises administering to a warm-blooded animal an effective amount of at least one agent, such as an antibody, saccharide or glycoconjugate as described above. In another embodiment, the method comprises administering to a warm-blooded animal an effective amount of at least one enzyme inhibitor (as described above) that inhibits the biosynthesis of sialyl Le^(a) or di-sialyl Le^(a) by malignant cells. It will be evident to those skilled in the art how to determine the optimal effective dose for a particular agent or enzyme inhibitor, e.g., based upon in vitro and in vivo studies in non-human animals. A variety of routes of administration may be used. Typically, administration will be intravenous, intracavitory (e.g., in pleural or peritoneal cavities), or in the bed of a resected tumor.

An agent may be administered as a composition, i.e., in combination with a pharmaceutically acceptable carrier or diluent, such as physiological saline. It will be recognized by those skilled in the art that an agent and a composition may be prepared in a sterile form. Moreover, an agent may be administered in combination with an immunotherapeutic or chemotherapeutic agent. When such a combination is desired, each substance may be administered sequentially, simultaneously, or combined and administered as a single composition. Diagnostic techniques, such as CAT scans for tumors, may be performed prior to and subsequent to administration to confirm effectiveness.

The following examples are offered by way of illustration and not by way of limitation.

EXAMPLES Example 1 GLYCOCONJUGATES AND ASSAYS

Synthetic glycoproteins (Neoglycoproteins)

Neoglycoproteins were produced by BioCarb AB (Lund, Sweden) by chemically coupling 10-20 moles of a specific oligosaccharide to 1 mole of nonglycosylated albumin, bovine (BSA) or human (HSA). The resulting synthetic glycoprotein (neoglycoprotein) contains multiple copies of the identical carbohydrate sequence, thereby producing a well characterized, mutivalent glycoconjugate which is extremely effective for studying carbohydrate-protein interactions. Depending on the size of the oligosaccharide, three different chemical spacer arms were used to couple the oligosaccharides to proteins 1) p-aminophenyl (PAP); 2) aminophenylethyl (APE); and 3) acetyl phenylene diamine were used to couple the shorter oligosaccharides to albumin since they will retain the anomeric configuration of the reducing sugars which may be involved in a potential binding site. APD was used to couple the larger sugars to protein by reductive amination, which converts the reducing sugar to an aminoalditol.

Direct Binding of Antibodies to Synthetic Glycoproteins (Neoglycoproteins)

Synthetic glycoproteins were coated onto microtiter plates by filling each well with 100 ng of the neoglycoprotein in 100 μl of 0.15 M sodium chloride, 0.01 M sodium phosphate, 0.1% sodium azide, pH 7.4, (PBS-azide) overnight at 4° C. Standard enzyme-linked immunoassays (ELISA) were then performed on the solid phase carbohydrate structures using the appropriate antibody diluted to 10 μg/ml.

Production of ELAM-1 cDNA transfected cell lines

L1-2/pMRB107 cells (L1-2^(ELAM-1)) were prepared by transfecting the ELAM-1 gene into the murine pre-B cell line L1-2 (Gallatin et al., Nature 304:30-34, 1983). A cDNA clone encoding ELAM-1 was obtained from a cDNA library made from activated human umbilical vein endothelial cell cultures by polymerase chain reaction (PCR) amplification. The ELAM-1 gene was inserted downstream of the hCMV promoter in pMRB101 [a derivative of EE6 which contains the E. coli cmt gene (Mulligan and Berg, Proc. Nat'l. Acad. Sci. USA 78:2072, 1981; Stephens and Corbett, N.A.R. 17:7110, 1989)]. DNA was introduced into L1-2 cells by electroporation and the cells selected for resistance to mycophenolic acid. A population of cells staining brightly for ELAM-1 were selected by FACS and cloned by limiting dilution. These cells are ELM-1^(hi) LFA-1^(mod) CD45^(hi) CD44^(neg) LECAM-₁ ^(neg), differing from the parent cell line or control vector transfectants only in their expression of ELAM-1. L1-2/pMRB101 (L1-2^(vector)) cells are a similarly transformed derivative of L1-2 transfected with pMRB101 and lacking ELAM-1 expression.

Cell Binding Assays

One hundred microliter samples of each synthetic glycoconjugate in phosphate buffered saline (PBS), pH 7.2, were absorbed onto glass wells of 8-chamber slides (LabTek) for two hours at RT. For some experiments glass slides were pre-coated with rabbit anti-human serum albumin (Sigma) at 200 μg/ml overnight at 4° C. and washed with PBS prior to the addition of the glycoconjugate. After blocking with 5% NBS/10 mM HEPES/Dulbecco's Modified Eagles Medium (DMEM), pH 7.0 (CM), L1-2^(ELAM-) 1 or L1-2^(vector) cells were applied to each well (1.5×10⁶ /0.15 ml in CM). After a 25 minute incubation at RT on a rotating shaker at 50 rpm, the tops of the wells were removed and the slides washed 3× in DMEM and then fixed by incubation in 1.5% glutaraldehyde (Kodak)/DMEM. Three to six 100× fields were counted for each data point.

Inhibition of Binding of ELAM-1 Containing Cells by Compounds

One hundred and twenty nanograms of Sialyl Le^(a) -HSA or Sialyl Le^(x) -HSA dissolved in 100 μl of phosphate-buffered saline were absorbed per well of an 8 chambered glass (LabTek) slide for 2 hours at room temperature. During this period, L1-2^(ELAM-1) cells were pre-incubated for 20 minutes on ice with increasing concentrations of Sialyl Le^(a) -HSA at 10⁷ cells/ml. After washing and blocking the wells in Complete Medium (CM, 5% normal bovine serum, 10 mM HEPES, pH 7.0, DMEM), L1-2^(ELAM-1) cells pre-incubated with compounds were added (1×10⁷ cells/ml) and incubated at room temperature while rotating at 50 rpm. After 25 minutes, slides were washed 3 times in Dulbecco's Modified Eagles Medium (DMEM) and then fixed in 1.5% glutaraldehyde/DMEM.

Example 2 CARBOHYDRATE STRUCTURE RECOGNIZED BY ELAM-1

The sensitive binding assay described in Example 1 uses cells permanently transfected with ELAM-1 cDNA. The mouse pre-B cell line, L1-2, transfected with ELAM-1 cDNA (L1-2ELAM 1), but not vector control cDNA, L1-2^(vector) expresses very high levels of ELAM-1. The ELAM-1 expressed by these cells is functional as L1-2^(ELAM-1) cells are adhesive for neutrophils and this adhesion is blocked by anti-ELAM-1 monoclonal antibodies. When added to glass slides coated with various synthetic glycoconjugates, L1-2^(ELAM-1) cells bound selectively to Sialyl Le^(a) and Sialyl Le^(x) neoglycoproteins, but not to a number of other glycoconjugates. L1-2^(ELAM-1) cells also bound, albeit more weakly, to Le^(a) neoglycoprotein. The binding to Le^(a) is significant as L1-2^(ELAM-1) cells bound poorly to Le^(x) and not at all to the glycoconjugates prepared with the structural analogs such as LNF I. That L1-2^(ELAM-1) cells did not bind other monosialylated carbohydrates, such as 3'SL, 6'SL, LSTa or LSTc demonstrates that the binding to Sialyl Le^(a) and Sialyl Le^(x) is not due to non-specific charge effects, but rather reflects specific structural features of these oligosaccharides. The low level of binding of ELAM-1 transfectants to Le^(a) is consistent with an essential role of fucose in recognition, but shows that neuraminic acid (also known as sialic acid) also plays a key role.

All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

From the foregoing, it will be evident that, although specific embodiments of the invention have been described herein for purposes of illustration, various modification may be made without deviating from the spirit and scope of the invention. 

We claim:
 1. A method for inhibiting within a biological preparation the binding of malignant cells expressing sialyl Le^(a) or di-sialyl Le^(a), to endothelial cells expressing a LEC-CAM, comprising:incubating the biological preparation with at least one agent that inhibits the binding of malignant cells expressing sialyl Le^(a) or di-sialyl Le^(a), to endothelial cells expressing a LEC-CAM, wherein said agent is selected from the group consisting of sialyl Le^(a), a carbohydrate portion of sialyl Le^(a), di-sialyl Le^(a), a carbohydrate portion of di-sialyl Le^(a), and a glycoconjugate that includes a carbohydrate portion of sialyl Le^(a) or di-sialyl Le^(a).
 2. A method for inhibiting within a biological preparation the binding of malignant cells expressing sialyl Le^(a) or di-sialyl Le^(a), to endothelial cells expressing ELAM-1, comprising:incubating the biological preparation with at least one agent that inhibits the binding of malignant cells expressing sialyl Le^(a) or di-sialyl Le^(a), to endothelial cells expressing ELAM-1, wherein said agent is selected from the group consisting of sialyl Le^(a), a carbohydrate portion of sialyl Le^(a), di-sialyl Le^(a), a carbohydrate portion of di-sialyl Le^(a), and a glycoconjugate that includes a carbohydrate portion of sialyl Le^(a) or di-sialyl Le^(a).
 3. A method for inhibiting within a biological preparation the binding of malignant cells expressing sialyl Le^(a), di-sialyl Le^(a) or sialyl Le^(x), to endothelial cells expressing a LEC-CAM, comprising:incubating the biological preparation with at least one agent capable of reacting with both sialyl Le^(a) and sialyl Le^(x), wherein said agent is selected from the group consisting of sialyl Le^(a), a carbohydrate portion of sialyl Le^(a), di-sialyl Le^(a), a carbohydrate portion of di-sialyl Le^(a), and a glycoconjugate that includes a carbohydrate portion of sialyl Le^(a) or di-sialyl Le^(a).
 4. A method for inhibiting within a biological preparation the binding of malignant cells expressing sialyl Le^(a), di-sialyl Le^(a) or sialyl Le^(x), to endothelial cells expressing ELAM-1, comprising:incubating the biological preparation with at least one agent capable of reacting with both sialyl Le^(a) and sialyl Le^(x), wherein said agent is selected from the group consisting of sialyl Le^(a), a carbohydrate portion of sialyl Le^(a), di-sialyl Le^(a), a carbohydrate portion of di-sialyl Le^(a), and a glycoconjugate that includes a carbohydrate portion of sialyl Le^(a) or di-sialyl Le^(a). 